Add wrong-t checker for incorrect testing.T usage in testify assertions

.golangci.yml

@@ -112,6 +112,9 @@ linters:
             - pkg: golang.org/x/tools/go/analysis
               desc: Please, implement helpers without usage of x/tools
 
+    exhaustive:
+      default-signifies-exhaustive: true
+
     forbidigo:
       forbid:
         - pattern: panic

README.md

@@ -113,6 +113,7 @@ https://golangci-lint.run/docs/linters/configuration/#testifylint
 | [suite-subtest-run](#suite-subtest-run)             | ✅                  | ❌       |
 | [suite-thelper](#suite-thelper)                     | ❌                  | ✅       |
 | [useless-assert](#useless-assert)                   | ✅                  | ❌       |
+| [wrong-t](#wrong-t)                                 | ✅                  | ❌       |
 
 > ⚠️ Also look at open for contribution [checkers](CONTRIBUTING.md#open-for-contribution)
 
@@ -1240,6 +1241,58 @@ assert.LessOrEqual(0, uintVal)
 
 ---
 
+### wrong-t
+
+```go
+❌
+func TestFoo(t *testing.T) {
+    assert.Equal(nil, expected, actual)
+
+    u := &testing.T{}
+    assert.Equal(u, expected, actual)
+}
+
+func TestBar(t *testing.T) {
+    a := assert.New(t)
+
+    t.Run("subtest", func(t *testing.T) {
+        a.Equal(expected, actual) // a was created with the outer t
+    })
+}
+
+✅
+func TestFoo(t *testing.T) {
+    assert.Equal(t, expected, actual)
+}
+
+func TestBar(t *testing.T) {
+    t.Run("subtest", func(t *testing.T) {
+        a := assert.New(t)
+        a.Equal(expected, actual)
+    })
+}
+```
+
+**Autofix**: false. <br>
+**Enabled by default**: true. <br>
+**Reason**: Protection from bugs and misleading test output.
+
+The checker handles two related cases of incorrect `testing.T` usage:
+
+#### 1) Nil or freshly created `testing.T` in package-level assertions
+
+Passing `nil` or a freshly allocated `&testing.T{}` / `new(testing.T)` as the `t` argument will
+cause a panic at runtime (nil dereference) or silently misattribute test failures.
+
+#### 2) Assertion object created with outer `t` used in a subtest
+
+When `assert.New(t)` or `require.New(t)` is called in an outer scope, the resulting
+`*Assertions` object is bound to the outer `testing.T`. Using it inside a `t.Run` subtest
+(which receives its own fresh `t`) causes test failures to be reported against the parent
+test rather than the subtest, breaking the display of test names in failure output.
+
+---
+
 ## Chain of warnings
 
 Linter does not automatically handle the "evolution" of changes.

analyzer/checkers_factory_test.go

@@ -62,6 +62,7 @@ func Test_newCheckers(t *testing.T) {
 		checkers.NewSuiteBrokenParallel(),
 		checkers.NewSuiteMethodSignature(),
 		checkers.NewSuiteSubtestRun(),
+		checkers.NewWrongT(),
 	}
 	allAdvancedCheckers := []checkers.AdvancedChecker{
 		checkers.NewBlankImport(),
@@ -71,6 +72,7 @@ func Test_newCheckers(t *testing.T) {
 		checkers.NewSuiteMethodSignature(),
 		checkers.NewSuiteSubtestRun(),
 		checkers.NewSuiteTHelper(),
+		checkers.NewWrongT(),
 	}
 
 	formatterWithoutEnabledOptions := checkers.RegularChecker(checkers.NewFormatter().

internal/checkers/checkers_registry.go

@@ -33,6 +33,7 @@ var registry = checkersRegistry{
 	{factory: asCheckerFactory(NewSuiteMethodSignature), enabledByDefault: true},
 	{factory: asCheckerFactory(NewSuiteSubtestRun), enabledByDefault: true},
 	{factory: asCheckerFactory(NewSuiteTHelper), enabledByDefault: false},
+	{factory: asCheckerFactory(NewWrongT), enabledByDefault: true},
 }
 
 type checkersRegistry []checkerMeta

internal/checkers/checkers_registry_test.go

@@ -60,6 +60,7 @@ func TestAll(t *testing.T) {
 		"suite-method-signature",
 		"suite-subtest-run",
 		"suite-thelper",
+		"wrong-t",
 	}
 	if !slices.Equal(expected, checkerList) {
 		t.Fatalf("unexpected list: %#v", checkerList)
@@ -98,6 +99,7 @@ func TestEnabledByDefault(t *testing.T) {
 		"suite-broken-parallel",
 		"suite-method-signature",
 		"suite-subtest-run",
+		"wrong-t",
 	}
 	if !slices.Equal(expected, checkerList) {
 		t.Fatalf("unexpected list: %#v", checkerList)